The present invention relates to an electronic organ of the institutional or classical type intended to simulate a pipe organ, and in particular to a transposition circuit therefor.
Present-day electronic organs generally fall into three classes: smaller home organs which are voiced to simulate a wide range of modern instruments but are not designed to closely simulate a pipe organ, electronic theater organs which simulate the characteristic sound of a theater pipe organ, and institutional or classical organs which simulate pipe organs generally found in churches and concert halls. Although classical pipe organ literature is best played on a true pipe organ, such organs are very expensive and require frequent maintenance to maintain the pipes in tune. Furthermore, changes in humidity and temperature affect the operation and sound of the organ, and the number of technicians who can maintain and tune pipe organs is rapidly dwindling. Consequently, pipe organs have become so expensive that they are beyond the means of most musicians and many churches.
In order to permit classical literature to be played, electronic organs have been developed which simulate, to varying degrees of closeness, the sound of a pipe organ. One approach is to utilize a pure digital system wherein the sounds produced by the various instruments are digitally stored in memories which are then addressed at a variable rate depending on the keys depressed to produce the tones of the instruments at the frequencies desired. Systems of this type have unique problems which prevent them from being completely satisfactory, however. Firstly, the number of harmonics as a function of the frequency of the wave form varies somewhat because of the limited number of sample points at low frequencies, and, secondly, aliasing is a significant problem. Other organs of this type utilize pure analog techniques where individual tone generators produce the various voices and complex switching arrangements are utilized to key the various tones. The circuitry and switching arrangement for such an organ is extremely complex and unwieldy, however, and this greatly increases the physical size and cost of the organ as well as posing significant maintenance problems. The third approach, and that which is employed in the present system, is to combine digital and analog techniques to utilize the advantages inherent in each of them.
In a pipe organ or an electronic organ simulating a pipe organ, the upper manual is referred to as the Swell manual because the volume of those voices was traditionally controlled by a swell chamber having a series of shutters which opened and closed under the control of the organist. The lower manual is referred to as the Great manual, and it, like the Swell manual, comprises sixty-one keys. The pedal manual comprises thirty-two pedals arranged in a convex pattern. The voice controls are referred to as stops and take the form of rocker tabs, blade-type tabs or drawbars.
Such organs also include a particular type of special effect control known as couplers, both intermanual and intramanual. Intermanual couplers enable voices normally assigned to one manual, including the pedalboard, to be played on another manual. For example, the pedalboard can be caused to play voices assigned to certain ranks of the Great manual, or the Swell manual may be coupled to the Great manual and vice versa. Intramanual couplers, on the other hand, enable expansion of the basic rank of pipes. For example, if an eight foot flute voice is played on the Great manual, and the four foot Great to Great coupler is activated, the organ will produce both the eight foot flute and the four foot flute. Likewise, if the sixteen foot Great to Great coupler is actuated, a sixteen foot flute will also be played.
A technique which is often employed in pipe and electronic organs is referred to as unification, which permits more ranks of pipes or voices to be produced without duplicating each pipe or voice in the rank. For example, a rank of diapasons at the eight foot level requires sixty-one pipes, and in a non-unified system, to add a rank of four foot diapasons, an additional sixty-one pipes would be necessary, for a total of one hundred twenty-two pipes. However, of the five octaves of four foot diapasons, four of them are exactly at the same pitch as the original eight foot rank diapasons, so that there are forty-eight redundant pipes. In a unified system, then, for each additional footage, only twelve pipes or keyers are added, so that for the combined two foot, four foot, eight foot and sixteen foot ranks, a total of only ninety-seven pipes or keyers are necessary. The disadvantage to this is that the chorus effect is not as pronounced, but this is offset by the very substantial cost savings.
Pipe organs are capable of producing voices known as mixtures, which comprise two to five or more pitches produced simultaneously by depressing a single key. The pitches are generally unison and mutation pitches, so that a 1 3/5 foot mixture comprises a 2 foot pitch, a 1 3/5 foot pitch, and a 1 foot pitch, for example. The rank of the mixture determines the pitches that are played, so depending where on the manual the key is depressed, the mixture will comprise either two unison and one mutation, as in the previous example, or two mutations and one unison. In this latter case, the mixture would comprise, for example, a 11/3 foot pitch, a 2 foot pitch, and a 22/3 foot pitch.
In an electronic organ of the type in question, there are, of necessity, a large number of interconnections between the manuals, keyswitches, couplers, stops, keyers and tone generators, which results in a very complex system. Such complexity greatly increases the cost of manufacturing and maintaining the organ and provides numerous opportunities for malfunctions to develop. In an attempt to reduce the complexity of electronic organs of this type, digital multiplexing techniques have been utilized wherein the manuals are scanned either sequentially or simultaneously to produce one or more serial data streams having keydown pulses in time slots corresponding to depressed keys of the manuals. A beneficial result of multiplexing is that the serial data streams can be manipulated to achieve coupling and footage generation. In the generation of footages, the data streams are selectively delayed in shift registers or the like so that keydown pulses are added to the data streams in those time slots corresponding to the footages desired, whether octavely or sub-octavely related. This technique of footage generation requires additional time slots in the data streams following scanning of the last key of each manual.
A feature which is often included in institutional organs is a transposer, which permits the key of the instrument to be changed to match music which is being played or sung together with the organ. For example, if a choir cannot easily sing a piece of music in the key that it is written, in the absence of a transposer, the organist would have to mentally transpose the music by one or more half steps, which requires a very high degree of skill. In earlier prior art organs, both true pipe organs and electronic organs, automatic transposition was accomplished by mechanically altering the physical relationship between the keys and the switches or other mechanical actuators which were operated when they were depressed. For example, the physical relation between the middle C key and the switches is changed so that when this key is depressed, the switch pertaining to C.music-sharp. would be actuated, in the case of transposition one-half step sharp. As will be appreciated, there is considerable mechanical complexity involved in providing for automatic transposition in this manner.
Further developments of automatic transposers involve the use of a variable frequency master oscillator which affects the frequencies of all of the divider outputs in the organ so that the absolute pitches of the tones will change but the relationship between the tones will remain constant. A disadvantage to this technique, however, is the instability of such a generator.
With the application of standard multiplexing techniques to the electronic organ field, the keyboard is scanned and a time division multiplexed serial data stream produced wherein keydown pulses appear in time slots corresponding to depressed keys of the keyboard. In organs of this type, transposition is accomplished by delaying the serial data stream by one or more time frames so that when the data is demultiplexed, the keydown pulses appear in time slots corresponding to those keys spaced from the depressed keys by the amount of transposition. A drawback to this technique is that, if it is desired to transpose in a direction opposite to that of the direction of scanning, an excessively long delay line is necessary. For example, if the keyboard is scanned from high to low, transposition flat can easily be accomplished by delaying the data stream by one or more time frames. If it is desired to transpose sharp, however, the data stream must be delayed until the next scan so that the keydown pulses appear in time slots which are perceived to occur before the original time slots. Since one stage of delay is required for every key of the manual, the delay line can become quite long, which adds to the cost of the organ.
A further disadvantage to the data stream delaying technique for accomplishing transposition is the difficulty of delaying each data stream by an equal amount in the case of plural manual organs wherein the serial data streams for the respective manuals are synchronized. A classical-type organ, for example, requires that the data stream from one manual be combined with the data streams from the other manuals so that synchronization thereof is necessary. Since a plurality of data streams must be delayed, and delayed by an equal amount, transposition thereof becomes unwieldy.
A further prior art technique for accomplishing transposition in a multiplexed organ is to delay the synchronizing or latch pulse signal which controls the serial to parallel conversion. Again, if transposition is in a direction opposite to the direction of scanning, very long delay times are required.
A problem with transposition in a multiplexed system is that it is possible to transpose some of the keydown pulses to time slots outside the range of tones which are capable of being played by the organ. For example, if the manual is scanned from high to low and the sixteen foot or thirty-two foot tone is being played by depressing the lowest key on the manual, transposition of this note flat by even one time slot would carry it outside the range of the organ. Thus, there would be no stages in the demultiplexer for a keydown pulse occurring at this time. If no extra time slots are provided at the upper and lower ends of the data stream, then transposition on the end of the data stream would cause the note to sound at the opposite end of the musical scale encompassed by the manual. One prior art attempt to solve this problem is to fold the actual tones which are produced to an octave higher or lower as by a switching matrix. A disadvantage to this solution, however, is that a number of switches are required to accommodate the various amounts of transposition, and any switching which is accomplished in the output circuitry of the organ is likely to cause undesirable transients.